The invention involves a swingable (slewable) tracker that can optionally detect in the optical, infra-red or radar wavelength and accordingly manifests an optical component and a detector component and/or a radar antenna component, and that preferably is equipped with an optical component for use in the IR range, which is constructed as a corrected mirror optic, preferably a Cassegrain optic with a large entry aperture. The tracker typically is used in the IR range as a homing head for a missile, preferably an unmanned one with a cruise engine or a similar missile, to acquire and/or engage fixed and/or moving targets, like helicopters or similar vehicles. The homing optic is housed in a movable manner by means of a two-axis, cardanic, roll-pitch-tracking system in an exterior housing rigidly connected to the missile structure and electro-mechanically executes the tracking and scanning motions that serve to acquire the target.
From the state of technology it is known how to use electro-mechanical, two-axis reference systems to track optical systems, like cameras among other things, for infra-red homing heads of missiles and the like. As a rule, two-axis reference systems are generally used in the process.
A widely used construction principle is the combination of a pitch and a yaw reference in conjunction with an external cardanic reference, whereby "pitch" means a turning motion of the optical system around the tracker's fixed Y axis and "yaw, a turning motion of the optical system around the tracker's fixed Z axis. The fixed coordinate system is thereby usually defined by the construction location of the tracker which is characterized as a rule by the axes being parallel to the fixed missile axes. The deflection angles describe movements around the tracker's fixed coordinate axes. The angles are measured outward from the non-moving, tracker construction location.
In such systems the deflection angles, also called squint angles, of the optical system can be determined very easily. With an exterior cardanic system the corresponding angles can be measured conventionally in conjunction with distance sensors on exterior positions. Because of the possible large separation between the distance sensor and the rotation axis, significant distance changes occur in response to angular changes which, as a rule, make it possible to achieve satisfactory measurement resolution (pick-up accuracy) by the deflection angle sensors. Another advantage of the exterior cardanic system consists of the pick-up and moment indicators being decoupled, i.e., motion in the pitch axis does not couple with the yaw pick-up and vice-a-versa. Systems of this type have been known for a long time.
A disadvantage of the arrangement described consists of there being only limited available construction room for the optical system because of its exterior location. Thus normally for a given light intensity (entrance aperture) the construction area required is somewhat greater than the operational capability of the optical system (volume of the tracker optic). Another disadvantage is the large amount of moving parts which is caused by the required size of the pitch and yaw frames of references as a well as the large bearing surfaces. The large number of moving parts and, as a rule, the higher bearing friction lead to correspondingly high positioning power and a significant energy requirement when the optical system has to be moved or tracks an object, whereby a lot of problems result especially when used in the tracking systems of missiles of the type described at the outset.
Another roll-pitch-tracking system is known which is also constructed as an external cardanic system. Here there are also similar problem areas. The rolling, i.e. the turning motion of the optical system around the fixed missile X axis, is hereby made possible by an externally located rolling contact bearing, whereby, however, there is also a large mass to be moved and a correspondingly high positioning power and significant energy requirement. The externally located rolling contact bearing can also lead to limitations in the available construction volume for the reasons already discussed above.
An interior cardanic solution brings significant improvements with respect to the problem areas previously described. It is known to take the form of a pitch-yaw-tracking system which is constructed as an internal cardanic system, wherein the mechanical reference frame system are disposed in the interior area of the tracker. Because of the smaller bearing surfaces, the available construction volume, especially with regard to the entrance aperture, can be better utilized and is smaller overall. Simultaneously all moving parts, especially the bearing and reference frame parts, can be constructed with more favorable weight, whereby the required positioning power as well as the resultant bearing friction are smaller. On the other hand, the squint angle pick-ups can certainly no longer be constructed in a simple fashion with the state of technology associated with internal cardanic systems. Also, with the use of an interior cardanic system, there is no possibility, as a rule, of measuring the squint angles in the area of the interior bearings, since the available construction volume is too small to house the sensors in the area of the interior cardanic system.
Thus as a general rule, a displacement of the angle pick-up sensors to the external area of the seeker or tracker head is sought. Here, too, the attainable measurement quality is limited by the coupling of the pitch and yaw motions of the cardanic frame of reference. By displacing the angle pick-up sensors to the exterior (away from the rotational axes) a turning motion around a tracker axis automatically leads to an influencing of the angle measurement around the correspondingly opposite cardanic axis. The pick-up of the pitch axis is simultaneously influenced by a yaw motion and vice-a-versa. These non-linear coupling effects cause technical measurement problems with respect to a high degree of pick-up accuracy and are recognized as increased "noise" in the subsequent correction of the angle measurement. Another problem of the pitch-yaw-reference system in an interior cardanic version consists of the squint angle range being limited by the primary mirror "striking" the rolling-contact-bearing housing. This problem can be minimized by a conceivable, asymmetrical mounting of the entire seeker head in the missile structure, yet this measure is not ever considered because of technical guidance reasons, since severe limitations could result for the operating range of the tracker because of the asymmetrical squint angle.